Clinton, the Democratic presidential nominee, was hit with a double whammy of questions about her private email server at State, first by host Matt Lauer and then by a veteran at the town hall-style event on NBC News.

Lauer kicked things off by asking Clinton to explain why her careless handling of classified information — which included discussions about America's covert drone program — shouldn't disqualify her from serving in the White House.

"I make no excuses for it," Clinton said of her use of a private email server. "It was something that should not have been done."

"But the real question is the handling of classified material ... and for all the viewers ... I have a lot of experience dealing with classified material."

Pressed by Lauer whether some of those emails had to do with the covert drone program, Clinton said: "Yes. Because of course there were no discussions of any of the covert actions in process being determined about whether or not to go forward.

"But every part of our government had to deal with questions and the secretary of State's office was first and foremost."

She pointed out that the FBI mentioned the drone program in its unclassified report on its investigation of her email setup.

After Lauer's questioning, a man who described himself as a veteran and a Republican said that when he worked in the military, he had to handle top secret information. He wanted to know why people like him should trust Clinton with America's most sensitive information.

Clinton responded that classified information has clear labeling and she insisted that she took the utmost care with secret information when she was head of State, launching into a lengthy explanation of classification markings and precautions she took as Lauer tried to cut in to move on to the next topic.